Cooled airfoil

ABSTRACT

A hollow air-cooled turbine blade or vane includes a liner for bringing cooling air into the blade and discharging it through two cooling air exhaust tubes disposed near the interior of the leading edge and extending spanwise of the blade. These tubes define between them a slot nozzle for discharge of air from the liner for impingement cooling of the leading edge. The exhaust tubes have air entrance holes adjacent the leading edge. The pressure drop to cause the circulation of the air out through the tubes is caused by centrifugal force or pressure drop across the stage or both.

4 1 Dec. 25, 1973 United States Patent [191 Aspinwall COOLED AIRFOIL[75] Inventor: Robert H. Aspinwall, Zionsville, lnd. PrimaryEmmmef-Evejrette Powell Attorney-Paul Fitzpatrick et al. [73] Assignee:General Motors Corporation,

Detroit, Mich.

[22] Filed: Sept. 15, 1972 liner for bringing cooling air into the bladeand dis- [21] Appl. No.: 289,417

charging it through two cooling air exhaust tubes disposed near theinterior of the leading edge and extending spanwise of the blade. Thesetubes define be- 416/97, 415/115, 416/96 [51] Int.

Fold 5/18 tween them a slot nozzle for discharge of air from the 416/92,96, 97, 95; liner for impingement cooling of the leading edge. Theexhaust tubes have air entrance holes adjacent the leading edge. Thepressure drop to cause the circula- [58] Field of Search ReferencesCited tion of the air out through the tubes is caused by cen- UNITEDSTATES PATENTS trifugal force or pressure drop across the stage or both.

3,032,314 416/96 X 3,574,481 Pyne et 416/97 X 4 Claims, 4 DrawingFigures COOLED AIRFOIL My invention is directed to improved cooledturbine blades and the like and is particularly directed to improvedstructures employing the principles of convectionand impingementcooling. As used here, the term convection cooling refers to thetransfer of heat from the interior of ablade wall to a cooling mediumflowing along the wall: Impingement cooling is a variation of convectioncooling in which the cooling medium is directed as a sheet or jet towardthe wall to be cooled, thereby improving the efficiency of the heattransfer or providing for increased heat transfer in particularlocalities such, for example, as the leading edge of a blade. Theinvention is particularly concerned with improvements in the cooling ofthe blade leading edge and with improved structure of a blade liner forthis purpose.

Convection cooling of a blade wall, as distinguished from impingementcooling, is described in Zimmerman U.S. Pat. No. 2,859,011, Nov. 4,1958, and Emerson et al. U.S. Pat. No. 3,446,480, May 27, 1969.Impingement cooling by air spouting from blade liners against the wallof a blade is described in Weise et al. U.S. Pat. No. 2,873,944, Feb.17, 1959. A blade including a liner with special provisions for jettingair to the leading edge of the blade for impingement cooling isdisclosed in Giesman et al. U.S. Pat. No. 3,635,587, Jan. 18, 1972.

According to my invention, impingement cooling of the leading edge of ablade is accomplished by jetting air from a slot nozzle which is definedby two tubes which serve to discharge at least a considerable part ofthe leading edge impingement cooling air from the blade so that this airdoes not flow past other portions of the blade wall, which are cooled byother means, and interfere with such cooling.

The principal object of my invention is to improve the cooling of gasturbine airfoils such as blades and vanes and to provide structure whichis readily fabricated and is particularly suitable for such a purpose.

The nature of my invention and its advantages will be apparent to thoseskilled in the art from the succeeding detailed description andaccompanying drawings of preferred embodiments of the invention.

FIG. 1 is a fragmentary sectional view of a turbine wheel with a blademounted thereon.

FIG.'2 is a fragmentary enlarged axonometric view of the tip of theblade with parts cut away.

FIG. 3 is an enlarged transverse sectional view of the leading edge ofthe blade taken on the plane indicated by the line 3--3 in FIG. 1.

FIG. 4 is a sectional view of a turbine showing application of theinvention to turbine nozzle vanes.

Referring first to FIGS. 1 and 2, there is illustrated a turbine wheel 2having a rim 3 on which are mounted a ring of fluid-reacting members orblading members 4, commonly known as blades. Each blade comprises adovetail root 6, a stalk 7, a platform 8, and a blade proper or airfoil10. The airfoil is hollow and has a leading edge at 11, a trailing edgeat 12, a convex face or wall 14, and a concave face or wall 15, thesefaces extending from one edge to the other. A web 16 adjacent themaximum thickness zone of the blade joins the two faces or walls todefine with the blade wall a chamber 18 extending from the leading edgeto the web 16 and a chamber 19 extending from the web 16 to the trailingedge. These chambers extend spanwise of the blade through the platformand t the tip of the blade, which is partially closed by a tip closure20. The blade stalk provides a structure into which air may be admittedfrom adjacent the blade stalk and flow into the chambers in the airfoil10.

The blade root 6 is mounted in suitably serrated slots in the wheel rim3. The blade is retained and flow of fluid between the wheel rim andplatforms is prevented by two cover plates or rings of cover plates 26and 27. These cover plates may be unitary or segmented. The details areimmaterial to the invention. Such plates are shown in U.S. Pat. No.3,446,480 referred to above, and in White U.S. Pat. No. 3,034,298, May15, 1962, for example. Holes 28 in the plate 26 and 30 in the plate 27provide for entry of cooling air or other medium from a suitable source(not illustrated) into the space between the cover plates and the bladestalk, from which the fluid flows into the blade stalk and thus into thepassages 18 and 19. The fluid ultimately exhausts through openings 31and 32 in the blade tip closure 20 forward and rearward of the web 16,respectively. Also, preferably, the trailing edge of the blade is formedwith outlets such as slots 34 for exhaust of cooling air at this point.

The structure so far described may be considered as state of the art. Toindicate generally the scale of the drawings, the specific blade shownhas a chord of about two inches.

To provide for air impingement and better flow of the cooling air alongthe interior of the surface of the blade wall, blade liners 35 and 36are provided extending spanwise of the blade in chambers 18 and 19,respectively. These liners are open at the platform end of the blade andclosed at the 32, of the blade, and are made of very thin flexible heatresisting sheet metal, preferably about three to five thousandths inchthick. The liners are preferably spaced about twenty-five thousandthsinch from the blade wall. Each liner has numerous small holes orperforations distributed over its surface as indicated generally at 40in FIGS. 2, 4, and 5. These perforations may be about seven thousandthsinch in diameter. Air which flows from the liner through these holesimpinges against the inner surface of the blade wall and flows betweenthe blade wall and liner to the outlets at 31, 32 and 34.

The structure of the liner as so far described may be the same as thatshown and described in greater detail in my companion application DocketNo. A-l5,l6l. The details of the liner so far described are not asignificant part of the subject invention.

My present invention is concerned with the structure of the liner 35adjacent the leading edge of the airfoil to provide improved impingementcooling at this point. Referring to FIGS. 2 and 3, liner 35 includes twoparallel generally oval tubes 38 which extend spanwise of the blade fromone end to the other. These tubes are fixed to each other by spacedsheet metal spacers 42 which are thin in the spanwise direction of theblade so that, effectively, the opening between the two tubes 38 definesa slot nozzle 43. The walls of the liner 35 are bonded to the tubes asindicated at 44. The bonding in this case, as with the bond between thetwo tubes, may be a brazed or other joint.

The sheet of gas issuing from the slot nozzle 43 impinges on the bladeleading edge 11 and then is withdrawn through a row of holes 46 in theforward edges of tubes 38 into these tubes for discharge from theairfoil. As shown in FIG. 2, the tubes extend to the tip of the bladewhere the gas is discharged through the corresponding opening or pair ofopenings 48 in the blade closure 20 which register with the ends oftubes 38. In the case of a rotating stage such as the rotor stage shownin FIG. 1, the centrifugal force caused by rotation of the rotor and thenormally lower external pressure at the blade tip tends to eject the gasfrom the tubes 38 and thus provide a draft for drawing the warmedimpingement cooling air into the holes 46.

The point of this structure is that the air heated by the leading edgeof the blade, which has a high rate of heat transfer from the turbinemotive fluid, does not flow rearwardly or radially in the leading edgepassage interior of the blade wall, in which case it would tend tointerfere with the impingement heat transfer coefficient. Impingementeffects are reduced in the presence of cross flow and the cross flowremoval through the tubes 38 is of basic importance.

FIG. 4 illustrates the application of the invention to a turbine nozzlevane, the principal difference from the embodiment previously describedbeing that the structure is stationary and that the suction to draw theheated leading edge cooling air into the exhaust tubes is developed bythe pressure drop across the nozzle. FIG. 4 discloses in schematic orconventional fashion known turbine structure which may include a turbineouter case 50 in which is mounted a nozzle outer shroud 51 and the rotorshroud 52. The nozzle includes vanes or airfoils 54 extending from theouter shroud 51 to an inner shroud 55. The shroud 51, vanes 54, andshroud 55 define an arinular cascade or turbine nozzle 56 from which themotive fluid is discharged to a turbine rotor comprising blades mountedon wheel 2 which rotor structure may be as described above or may be ofany suitable nature.

The nozzle vanes have a leading edge 58 and a trailing edge 59 and theusual concave and convex faces joining these. Also, preferably, thenozzle vanes include a transverse web 60 adjacent the midchord of thevane. In general, the structure may be much the same as that describedwith respect to the blades 10 above except, of course, for thedifference in the mounting of the airfoil structure. A line 35, whichmay correspond to the liner 35 previously described, is mounted in thechamber ahead of the web 60 and is associated with discharge tubes 38 aspreviously described. FIG. 3 may be considered to depict a section ofthe forward edge portion of the vane 54.

In the case of the nozzle installation, cooling air, which may becompressor discharge air, is fed into a space 62 between the turbinecase and outer shroud 51 from which it flows through a hole 63 into eachvane liner 35. The air is ejected from the slot nozzle 43 and, aftercooling the leading edge, is withdrawn into the exhaust tubes 38 whichcommunicate with an outlet 64 in the inner shroud 55. Air thusdischarged flows into a space 66 between the inner shroud and an annularwall 67 which is blocked from compressor discharge pressure but is opento pressure downstream of the turbine nozzle through the gap 68 betweenthe nozzle and the turbine rotor. The leading edge impingement coolingair thus is circulated by virtue of the pressure drop across the turbinenozzle through the circuit just described. Impingement cooling fromopenings 40 in the liner may also occur as previously described. The airused for this impingement cooling may be discharged through any suitablylocated outlet in the surface or end of the vane.

It should be apparent to those skilled in the art that I have devised animproved arrangement for impingement cooling of the leading edge of aheated airfoil which minimizes interference by this impingement coolingair with other cooling air, and provides for vigorous circulation of theleading edge impingement cooling air.

The detailed description of preferred embodiments of the invention forthe purpose of explaining the principles thereof is not to be consideredas limiting or restricting the invention, since many modifications maybe made by the exercise of skill in the art.

I claim:

1. A cooled fluid-directing element for a turbomachine comprising, incombination, a wall defining a hollow airfoil having two faces and aleading edge joining the faces, means for conducting a cooling gas intothe airfoil, two cooling gas exhaust tubes disposed adjacent theinterior of the leading edge and extending spanwise of the airfoil to anoutlet at one end of the airfoil, the exhaust tubes defining betweenthem a slot nozzle for discharge of the cooling gas from the conductingmeans toward the interior of the leading edge, and the exhaust tubesdefining means for entry of the cooling gas into the tubes from near theleading edge.

2. A cooled fluid-directing rotor blade element for a turbomachinecomprising, in combination, a wall defining a hollow airfoil having twofaces and a leading edge joining the faces, the airfoil having a baseadapted for connection to a rotor and having a tip remote from the base,means for conducting a cooling gas into the airfoil, two cooling gasexhaust tubes disposed adjacent the interior of the leading edge andextending spanwise of the airfoil to an outlet at the tip end of theairfoil, the exhaust tubes defining between them a slot nozzle fordischarge of the cooling gas from the conducting means toward theinterior of the leading edge, and the exhaust tubes defining means forentry of the cooling gas into the tubes from near the leading edge.

3. A cooled fluid-directing nozzle vane installation for a turbomachinecomprising, in combination, a wall defining a hollow nozzle vane airfoilhaving two faces and a leading edge joining the faces, means forconducting a cooling gas into the airfoil, two cooling gas exhaust tubesdisposed adjacent the interior of the leading edge and extendingspanwise of the airfoil to an outlet at one end of the airfoil, theexhaust tubes defining between them a slot nozzle for discharge of thecooling gas from the conducting means toward the intenor of the leadingedge, and the exhaust tubes defining means for entry of the cooling gasinto the tubes from near the leading edge, the means for conducting thecooling gas into the element being subjected to pressure upstream of thenozzle vane and the exhaust tube outlet being subjected to pressuredownstream of the nozzle vane.

4. A cooled fluid-directing element for a turbomachine comprising, incombination, a wall defining a hollow airfoil having two faces and aleading edge joining the faces, means including a blade liner forconducting a cooling gas into the airfoil, two cooling gas exhaust tubesdisposed adjacent the interior of the leading edge and extendingspanwise of the airfoil to an outlet at one end of the airfoil, theexhaust tubes defining the leading edge portion of the blade liner anddefining between them a slot nozzle for discharge of the cooling gasfrom the liner toward the interior of the leading edge, and the exhausttubes having ports distributed along the tubes for entry of the coolinggas into the tubes from near the leading edge.

k 4 l t I

1. A cooled fluid-directing element for a turbomachine comprising, incombination, a wall defining a hollow airfoil having two faces and aleading edge joining the faces, means for conducting a cooling gas intothe airfoil, two cooling gas exhaust tubes disposed adjacent theinterior of the leading edge and extending spanwise of the airfoil to anoutlet at one end of the airfoil, the exhaust tubes defining betweenthem a slot nozzle for discharge of the cooling gas from the conductingmeans toward the interior of the leading edge, and the exhaust tubesdefining means for entry of the cooling gas into the tubes from near theleading edge.
 2. A cooled fluid-directing rotor blade element for aturbomachine comprising, in combination, a wall defining a hollowairfoil having two faces and a leading edge joining the faces, theairfoil having a base adapted for connection to a rotor and having a tipremote from the base, means for conducting a cooling gas into theairfoil, two cooling gas exhaust tubes disposed adjacent the interior ofthe leading edge and extending spanwise of the airfoil to an outlet atthe tip end of the airfoil, the exhaust tubes defining between them aslot nozzle for discharge of the cooling gas from the conducting meanstoward the interior of the leading edge, and the exhaust tubes definingmeans for entry of the cooling gas into the tubes from near the leadingedge.
 3. A cooled fluid-directing nozzle vane installation for aturbomachine comprising, in combination, a wall defining a hollow nozzlevane airfoil having two faces and a leading edge joining the faces,means for conducting a cooling gas into the airfoil, two cooling gasexhaust tubes disposed adjacent the interior of the leading edge andextending spanwise of the airfoil to an outlet at one end of theairfoil, the exhaust tubes defining between them a slot nozzle fordischarge of the cooling gas from the conducting means toward theinterior of the leading edge, and the exhaust tubes defining means forentry of the cooling gas into the tubes from near the leading edge, themeans for conducting the cooling gas into the element being subjected topressure upstream of the nozzle vane and the exhaust tube outlet beingsubjected to pressure downstream of the nozzle vane.
 4. A cooledfluid-directing element for a turbomachine comprising, in combination, awall defining a hollow airfoil having two faces and a leading edgejoining the faces, means including a blade liner for conducting acooling gas into the airfoil, two cooling gas exhaust tubes disposedadjacent the interior of the leading edge and extending spanwise of theairfoil to an outlet at one end of the airfoil, the exhaust tubesdefining the leading edge portion of the blade liner and definingbetween them a slot nozzle for discharge of the cooling gas from theliner toward the interior of the leading edge, and the exhaust tubeshaving ports distributed along the tubes for entry of the cooling gasinto the tubes from near the leading edge.